<title>The Euler function</title><link href="http://hzoi.com/tomorrow.css" rel="stylesheet"><div class="ui existing segment"><pre><code><span class="pl-cp">#include</span> <span class="pl-cpf">&lt;cstdio&gt;</span><span class="pl-cp"></span>
<span class="pl-cp">#include</span> <span class="pl-cpf">&lt;cstring&gt;</span><span class="pl-cp"></span>
<span class="pl-k">const</span> <span class="pl-kt">int</span> <span class="pl-n">N</span> <span class="pl-o">=</span> <span class="pl-mi">3000000</span> <span class="pl-o">+</span> <span class="pl-mi">10</span><span class="pl-p">;</span>
<span class="pl-kt">int</span> <span class="pl-n">a</span><span class="pl-p">,</span> <span class="pl-n">b</span><span class="pl-p">,</span> <span class="pl-n">prime</span><span class="pl-p">[</span><span class="pl-n">N</span><span class="pl-p">],</span> <span class="pl-n">fi</span><span class="pl-p">[</span><span class="pl-n">N</span><span class="pl-p">];</span>
<span class="pl-kt">bool</span> <span class="pl-n">is_prime</span><span class="pl-p">[</span><span class="pl-n">N</span><span class="pl-p">];</span>
<span class="pl-kt">void</span> <span class="pl-nf">sieve</span><span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">n</span><span class="pl-p">)</span> <span class="pl-p">{</span>
    <span class="pl-n">memset</span><span class="pl-p">(</span><span class="pl-n">is_prime</span><span class="pl-p">,</span> <span class="pl-mi">1</span><span class="pl-p">,</span> <span class="pl-k">sizeof</span><span class="pl-p">(</span><span class="pl-n">is_prime</span><span class="pl-p">));</span>
    <span class="pl-n">is_prime</span><span class="pl-p">[</span><span class="pl-mi">1</span><span class="pl-p">]</span> <span class="pl-o">=</span> <span class="pl-nb">false</span><span class="pl-p">;</span>
    <span class="pl-k">for</span> <span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">i</span> <span class="pl-o">=</span> <span class="pl-mi">2</span><span class="pl-p">;</span> <span class="pl-n">i</span> <span class="pl-o">&lt;=</span> <span class="pl-n">n</span><span class="pl-p">;</span> <span class="pl-n">i</span><span class="pl-o">++</span><span class="pl-p">)</span> <span class="pl-p">{</span>
        <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-n">is_prime</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">])</span> <span class="pl-p">{</span>
            <span class="pl-n">prime</span><span class="pl-p">[</span><span class="pl-o">++</span><span class="pl-n">prime</span><span class="pl-p">[</span><span class="pl-mi">0</span><span class="pl-p">]]</span> <span class="pl-o">=</span> <span class="pl-n">i</span><span class="pl-p">;</span>
            <span class="pl-n">fi</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">]</span> <span class="pl-o">=</span> <span class="pl-n">i</span> <span class="pl-o">-</span> <span class="pl-mi">1</span><span class="pl-p">;</span>
        <span class="pl-p">}</span>
        <span class="pl-k">for</span> <span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">j</span> <span class="pl-o">=</span> <span class="pl-mi">1</span><span class="pl-p">;</span> <span class="pl-n">j</span> <span class="pl-o">&lt;=</span> <span class="pl-n">prime</span><span class="pl-p">[</span><span class="pl-mi">0</span><span class="pl-p">]</span> <span class="pl-o">&amp;&amp;</span> <span class="pl-n">i</span> <span class="pl-o">*</span> <span class="pl-n">prime</span><span class="pl-p">[</span><span class="pl-n">j</span><span class="pl-p">]</span> <span class="pl-o">&lt;=</span> <span class="pl-n">n</span><span class="pl-p">;</span> <span class="pl-n">j</span><span class="pl-o">++</span><span class="pl-p">)</span> <span class="pl-p">{</span>
            <span class="pl-n">is_prime</span><span class="pl-p">[</span><span class="pl-n">i</span> <span class="pl-o">*</span> <span class="pl-n">prime</span><span class="pl-p">[</span><span class="pl-n">j</span><span class="pl-p">]]</span> <span class="pl-o">=</span> <span class="pl-nb">false</span><span class="pl-p">;</span>
            <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-n">i</span> <span class="pl-o">%</span> <span class="pl-n">prime</span><span class="pl-p">[</span><span class="pl-n">j</span><span class="pl-p">]</span> <span class="pl-o">==</span> <span class="pl-mi">0</span><span class="pl-p">)</span> <span class="pl-p">{</span>
                <span class="pl-n">fi</span><span class="pl-p">[</span><span class="pl-n">i</span> <span class="pl-o">*</span> <span class="pl-n">prime</span><span class="pl-p">[</span><span class="pl-n">j</span><span class="pl-p">]]</span> <span class="pl-o">=</span> <span class="pl-n">prime</span><span class="pl-p">[</span><span class="pl-n">j</span><span class="pl-p">]</span> <span class="pl-o">*</span> <span class="pl-n">fi</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">];</span>
                <span class="pl-k">break</span><span class="pl-p">;</span>
            <span class="pl-p">}</span> <span class="pl-k">else</span>
                <span class="pl-n">fi</span><span class="pl-p">[</span><span class="pl-n">i</span> <span class="pl-o">*</span> <span class="pl-n">prime</span><span class="pl-p">[</span><span class="pl-n">j</span><span class="pl-p">]]</span> <span class="pl-o">=</span> <span class="pl-p">(</span><span class="pl-n">prime</span><span class="pl-p">[</span><span class="pl-n">j</span><span class="pl-p">]</span> <span class="pl-o">-</span> <span class="pl-mi">1</span><span class="pl-p">)</span> <span class="pl-o">*</span> <span class="pl-n">fi</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">];</span>
        <span class="pl-p">}</span>
    <span class="pl-p">}</span>
<span class="pl-p">}</span>
<span class="pl-kt">int</span> <span class="pl-nf">main</span><span class="pl-p">()</span> <span class="pl-p">{</span>
    <span class="pl-n">sieve</span><span class="pl-p">(</span><span class="pl-mi">3000000</span><span class="pl-p">);</span>
    <span class="pl-k">while</span> <span class="pl-p">(</span><span class="pl-o">~</span><span class="pl-n">scanf</span><span class="pl-p">(</span><span class="pl-s">&quot;%d%d&quot;</span><span class="pl-p">,</span> <span class="pl-o">&amp;</span><span class="pl-n">a</span><span class="pl-p">,</span> <span class="pl-o">&amp;</span><span class="pl-n">b</span><span class="pl-p">))</span> <span class="pl-p">{</span>
        <span class="pl-kt">long</span> <span class="pl-kt">long</span> <span class="pl-n">ans</span> <span class="pl-o">=</span> <span class="pl-mi">0</span><span class="pl-p">;</span>
        <span class="pl-k">for</span> <span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">i</span> <span class="pl-o">=</span> <span class="pl-n">a</span><span class="pl-p">;</span> <span class="pl-n">i</span> <span class="pl-o">&lt;=</span> <span class="pl-n">b</span><span class="pl-p">;</span> <span class="pl-n">i</span><span class="pl-o">++</span><span class="pl-p">)</span> <span class="pl-n">ans</span> <span class="pl-o">+=</span> <span class="pl-n">fi</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">];</span>
        <span class="pl-n">printf</span><span class="pl-p">(</span><span class="pl-s">&quot;%lld</span><span class="pl-se">\n</span><span class="pl-s">&quot;</span><span class="pl-p">,</span> <span class="pl-n">ans</span><span class="pl-p">);</span>
    <span class="pl-p">}</span>
<span class="pl-p">}</span>
</cpde></pre></div>